Effect of tumor cell heterogeneity on receptor engagement MPIs: Barroso, Corr and Intes ABSTRACT Precision medicine in oncology has shown great promise in improving patient prognosis and well-being. However, current clinical targeted therapies that act on specific molecular targets associated with cancer have been less effective than anticipated, mainly due to intrinsic and/or relatively rapid acquisition of resistance. Cellular heterogeneity, in particular tumor/stroma compositional heterogeneity and variations in the expression of membrane-bound receptors, has been implicated as an important driver of resistance to anti-cancer treatments. Though, to date, no analytical tool can provide means to replicate these heterogeneities in vitro and can monitor quantitatively the binding of therapeutic antibodies or drug-antibody conjugates to their respective targets, which is critical for drug deliver efficacy. Herein, we propose to integrate a biomanufacturing platform with 3D optical molecular imaging to investigate, for the first time, the influence of tumor cell heterogeneity, namely compositional heterogeneity as well as receptor level expression heterogeneity (i.e., Her2+, EGFR and Tfn), on target-receptor engagement. The unique characteristics of our approach are the ability to manufacture on demand ?histology grade? 3D heterogeneous breast tumor systems and quantify ligand-receptor engagement in these systems beyond the current depth limits of microscopy. To achieve our goals, we have assembled a multidisciplinary research team with established expertise and collaboration track record in all facets on the program. Upon completion of this project, we will have integrated this analytical platform to assess receptor engagement of well-known drug carriers in heterogeneous 3D cancer systems. This platform is expected to advance personalized medicine by providing tools and approaches that can be used to critically assess tailored therapy management strategies.